a) Field of the Invention
The present invention relates to semiconductor switching devices, and more particularly to static induction type semiconductor switching devices.
b) Description of the Prior Art
The static induction transistor was first proposed by Jun-ichi NISHIZAWA, one of the present inventors. In the static induction transistor, current control can be performed by controlling the height of a potential barrier induced in front of the source in accordance with the voltages applied to the gate and to the drain, to thereby change the amount of the charge carriers injected from the source across the potential barrier into a current channel. In general, the static induction transistor, as is well known, has many advantages over conventional bipolar and unipolar transistors in such aspects as high transconductance, high blocking voltage, high operating speed, large current capacity and so on. A junction static induction transistor can be used in two operational modes: normally-on (depletion) mode and normally-off (enhancement) mode. In a normally-off mode static induction transistor, the gate is forward-biased to turn the transistor on, and therefore a certain amount of minority carriers are injected from the gate into the channel. Such a carrier injection from the gate serves to promote the injection of carriers (majority carriers for the current channel) from the source into the current channel, which will lead to an increase in the transconductance as well as the current gain of the transistor. If an excessively large amount of minority carriers are injected from the gate into the channel, however, those carriers may cause an undesirable carrier storage effect in the current channel, which storage effect naturally obstructs the otherwise high speed operation of the transistor.
A static induction transistor eliminates carrier storage effect caused by excessive minority carriers injected from the gate into the current channel has been disclosed by Jun-ichi NISHIZAWA in his U.S. Pat. No. 4,284,997. In this proposed static induction transistor, there is employed a split-gate structure which comprises a driving (or active) gate exclusively serving to control the carrier flow in the current channel in response to a control signal applied thereto, and a subsidiary non-driving (or passive) gate for absorbing carriers injected from the driving gate into the current channel.